1. Field of the Invention
The present invention relates to a lithographic apparatus and device manufacturing method using such a lithographic apparatus. The invention further relates to a radiation sensor for use in a lithographic apparatus, a lithographic apparatus comprising such a radiation sensor, and a device manufacturing method using such a lithographic apparatus. The invention further relates to a method of manufacturing a radiation sensor.
2. Description of the Related Art
A lithographic apparatus is a machine that applies a desired pattern onto a substrate, usually onto a target portion of the substrate. A lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs). In that instance, a patterning device, which is alternatively referred to as a mask or a reticle, may be used to generate a circuit pattern to be formed on an individual layer of the IC. This pattern can be transferred onto a target portion (e.g. comprising part of, one, or several dies) on a substrate (e.g. a silicon wafer). Transfer of the pattern is typically via imaging onto a layer of radiation-sensitive material (resist) provided on the substrate. In general, a single substrate will contain a network of adjacent target portions that are successively patterned. Known lithographic apparatus include steppers, in which each target portion is irradiated by exposing an entire pattern onto the target portion at one time, and scanners, in which each target portion is irradiated by scanning the pattern through a radiation beam in a given direction (the “scanning” direction) while synchronously scanning the substrate parallel or anti-parallel to this direction. It is also possible to transfer the pattern from the patterning device to the substrate by imprinting the pattern onto the substrate.
It has been proposed to immerse the substrate in the lithographic projection apparatus in a liquid having a relatively high refractive index, e.g. water, so as to fill a space between the final element of the projection system and the substrate. This enables imaging of smaller features.
A number of sensors are typically used at substrate level for evaluating and optimizing imaging performance. These may include an integrated lens interferometer at scanner, i.e. ILIAS. The ILIAS is an interferometric wavefront measurement system that may perform static measurements on lens aberrations up to a high order. It comprises a source module and a sensor module.
The source module may comprise a patterned layer of chromium that is placed in an object plane of a projection system of the lithographic apparatus and may have additional optics provided above the chromium layer. The source module of ILIAS provides a wavefront of radiation to the entire pupil of the projection system.
The sensor module may comprise a patterned layer of chromium, which is placed in an image plane of the projection system, and a camera that is placed some distance behind the layer of chromium. The patterned layer of chromium of the sensor module diffracts incident radiation into several diffraction orders that interfere with each other giving rise to a interferogram. The interferogram is measured by the camera. Aberrations in the projection system may then be determined by software based upon the interferogram as measured with the camera.
The ILIAS may be implemented as an integrated measurement system used for system initialization and calibration. Alternatively, it may be used for monitoring and recalibration “on-demand”. A conventional ILIAS is not optimized for use in systems with high numerical aperture (NA), i.e. a liquid immersion system.